Eggs are a staple in almost every kitchen, prized for their versatility, protein content, and essential role in baking. However, they are also one of the most common sources of confusion when it comes to food safety. Most of us have stood in front of the refrigerator, carton in hand, wondering if those eggs from three weeks ago are still safe to scramble. Understanding the difference between a printed date and actual spoilage is key to reducing food waste while keeping your family safe.
Understanding Egg Dates and Labeling
The first step in determining egg freshness is deciphering the numbers stamped on the carton. These dates can be misleading because they often refer to quality rather than safety.
Sell By vs. Use By Dates
A Sell By date tells the retailer how long to keep the item on the shelf. It is not an expiration date for the consumer. In many cases, eggs remain perfectly safe to eat for several weeks after this date has passed, provided they have been handled and stored correctly. A Use By or Best If Used By date is a suggestion from the manufacturer regarding when the eggs will be at their peak flavor and textural quality. After this date, the whites might become thinner or the yolks more fragile, but they are not necessarily “bad.”
The Julian Date
If you look closely at a USDA graded egg carton, you will see a three digit code next to the plant number. This is the Julian date, representing the day of the year the eggs were washed and packed. For example, 001 represents January 1 and 365 represents December 31. This is the most accurate way to know exactly how old your eggs are. Generally, eggs are good for 4 to 5 weeks beyond this pack date.
The Science of Egg Spoilage
To know how to tell if an egg is expired, it helps to understand what happens inside the shell over time. Eggshells are porous, meaning they have thousands of tiny holes that allow air and moisture to move in and out.
As an egg ages, moisture evaporates through these pores, and air enters to take its place. This creates an increasingly large air cell at the blunt end of the egg. Simultaneously, the chemical structure of the egg white, or albumen, begins to break down. The thick white becomes watery, and the chalazae, those white stringy bits that hold the yolk in place, weaken. This is why older eggs spread out more in a pan compared to fresh eggs, which sit high and tight.
The Float Test for Freshness
The float test is perhaps the most popular DIY method for checking egg age. It relies entirely on the size of the air cell mentioned previously.
To perform this test, fill a bowl or deep glass with cold water and gently drop the egg in. If the egg sinks to the bottom and lays flat on its side, it is very fresh. If the egg stays on the bottom but stands up on one end, it is older but still safe to eat. If the egg floats to the surface, it has developed a large air cell and is likely quite old. While a floating egg is a strong indicator of age, it is not a definitive proof of spoilage. It simply means you should proceed to the next, more direct sensory tests.
The Sniff Test: The Gold Standard
If you are unsure after the float test, the sniff test is the most reliable way to identify a truly spoiled egg. A rotten egg has a very distinct, pungent odor caused by the buildup of hydrogen sulfide gas.
To perform this test properly, do not rely on smelling the egg through the shell. Crack the egg into a clean white bowl or saucer. If it has a neutral scent, it is fine. If it emits an unmistakable “sulfur” or “rotten” smell, discard it immediately and wash the bowl thoroughly with hot, soapy water. This smell will be present whether the egg is raw or cooked.
Visual Inspection After Cracking
Once you have cracked the egg, look for visual cues that indicate spoilage or bacterial growth.
A fresh egg will have a bright yellow or orange yolk and a thick white that doesn’t spread much. An older but safe egg will have a flatter yolk and watery whites. However, if you notice any discoloration in the white, such as a pink, iridescent, or green hue, this is a sign of Pseudomonas bacteria, and the egg must be tossed. Similarly, black or green spots inside the egg indicate mold growth.
You might occasionally see a small red spot on the yolk. This is a blood spot caused by a ruptured blood vessel in the hen’s ovary during the laying process. These are not a sign of spoilage and are perfectly safe to eat, though you can spoon them out if they unappealing to you.
Proper Storage to Extend Shelf Life
How you store your eggs greatly impacts how quickly they expire. In the United States and several other countries, eggs are washed and sanitized commercially, which removes the natural protective coating called the bloom. Because of this, they must be refrigerated to prevent bacterial growth.
Temperature Consistency
Eggs should be stored at a consistent temperature of 40 degrees Fahrenheit or below. It is a common mistake to store eggs in the built in racks on the refrigerator door. The door is the warmest part of the fridge and is subject to frequent temperature fluctuations every time you open it. Instead, keep the eggs in their original carton on an internal shelf, preferably toward the back.
The Original Carton
The carton serves two purposes: it protects the eggs from breaking and it prevents them from absorbing strong odors from other foods in the fridge, like onions or fish. Since eggshells are porous, they act like little sponges for smells. Keeping them sealed in the carton keeps your breakfast tasting like eggs rather than last night’s leftovers.
Safety Risks of Expired Eggs
The primary concern with eating expired or improperly handled eggs is Salmonella. This bacteria can be present on the shell or inside the egg itself. While refrigeration slows the growth of bacteria, it does not kill it.
Cooking is the final line of defense. To ensure safety, eggs should be cooked until both the white and the yolk are firm. For dishes containing eggs, the internal temperature should reach at least 160 degrees Fahrenheit. If you are using older eggs, it is best to use them in hard boiled preparations or baked goods rather than eating them over easy or poached.
Egg Math and Quality Calculation
If you are curious about the rate of quality decline, you can think of it in terms of Haugh units, which measures the height of the albumen relative to the weight of the egg. While you don’t need a lab at home, a simple way to track your “freshness window” is using a basic day count formula.
If Today is Day T and Julian Date is Day J, the freshness age A is:
A = T – J
If A is less than 28, the egg is in its peak quality phase. If A is between 28 and 45, the egg is in its standard edible phase. If A is greater than 45, you should perform a sniff test before use.
In a hypothetical scenario where you track the degradation rate D as a function of temperature Temp and Time t, the formula might look like:
D = (t x Temp) / 100
This shows that as temperature increases, the speed of degradation multiplies, emphasizing why leaving eggs on the counter is a recipe for quick spoilage.
Summary of Best Practices
To summarize, never rely solely on the date stamped on the box. Use the float test as a preliminary screen, but always trust your nose. If an egg smells bad, it is bad. If the white is discolored or shows signs of mold, discard it. By storing eggs in the coldest part of your refrigerator in their original container, you can often enjoy them safely for up to five weeks past the pack date.
FAQs
Can I eat eggs that are two weeks past the Sell By date?
Yes, in most cases, eggs are perfectly safe to eat for three to five weeks after you bring them home, which usually extends well past the Sell By date. As long as they have been kept refrigerated at 40 degrees Fahrenheit or lower and pass the sniff test, they are fine for consumption.
Why do some eggs float while others sink?
Eggs float because of the air cell that forms between the shell and the membrane. As an egg ages, it loses moisture and carbon dioxide through the pores in the shell, causing the air pocket to expand. A floating egg is simply a very old egg, but it only becomes “expired” or unsafe if bacteria have entered and caused spoilage.
What should I do if I find a blood spot in my egg?
Blood spots are not a sign of a bad egg or a fertilized egg. They are simply caused by a small blood vessel rupture during the egg’s formation. They are safe to eat, though you can remove the spot with the tip of a knife if you prefer for aesthetic reasons.
Is it safe to wash eggs before putting them in the fridge?
No, you should not wash eggs at home. Commercial eggs in the United States are already washed and then coated with a thin layer of mineral oil to replace the natural bloom. If you wash them again, you may push bacteria through the porous shell into the egg itself.
Can I freeze eggs that are about to expire?
Yes, you can freeze eggs to extend their life for up to a year, but you must crack them out of their shells first. You can freeze whole eggs by lightly beating the yolk and white together, or freeze whites and yolks separately. Do not freeze eggs in the shell, as the liquid will expand and crack the shell, leading to contamination.